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Rocks of the mid‐Cretaceous Colorado allogroup and time‐equivalent strata (late middle Albian to early Campanian; ∼104 Ma to ∼83 Ma), are dominated by marine mudstone and siltstone that was deposited in a few tens of meters of water up to several hundred kilometers from shore. In the north and west, nearshore and coastal plain facies form relatively minor components of the allogroup. The rocks are divided into allomembers by marine transgressive and flooding surfaces. Allomembers are the fundamental genetic stratal packages, and typically span ∼50‐200 kyr. Allomembers are grouped into larger informal “units” (spanning ∼400‐800 kyr), and alloformations (spanning a few Myr). Except for the Cenomanian Dunvegan alloformation, rocks of the Colorado allogroup lack well‐developed clinoform stratification. The scarcity of clinoforms suggests that supply rate usually exceeded accommodation rate and …